A Crash Course in Tracking HABs

To simply see where balloons are and to track their course, go to the website: SpaceNear This site shows positions of balloons live with various telemetry. At the top left hand side is an info panel with current notes on launches and a link to the #highaltitude IRC channel. Over on the right hand side are various panels showing telemetry from payloads and chase vehicles if present. You can quickly pan to a particular balloon by clicking on ‘Pan To’ in it’s information box. The information shown in these panels is retrieved by many receiving stations which are denoted by the small tower icons on the map. These stations receive the telemetry directly (or remotely) from the balloon’s payload via radio and then feed it to the Habitat website. In the background, the Habitat website parses the telemetry string and feeds it to SpaceNear.us for display. Around each of the balloons on the map are two circles. The outer blue circle is the one degree footprint. This gives the range of the balloon approximately from ground level. The inner green circle is the five degree footprint. Using these two circles, you can get an idea of when you should be able to hear the telemetry from your receiving position.

When the signal is received by a receiving station, the audio is fed into a PC/Mac etc. or in the case of SDRs, routed from the SDR software to a program called dl-fldigi This is a special version of this program, specific to HAB. The radio is then tuned to the HAB, the most common band used being the 70cms band (430MHz). Two modes of sending the telemetry are used commonly, these are RTTY (Radio Teletype) and Domino. The settings can be entered manually but for scheduled flights, there is an easier way to configure the software. By selecting the list box to the left of ‘Browse All’ on the dl-fldigi front panel, a list of current flights is normally available. You can click on one of these and then click on Auto-Configure. This sets the software up for the payload that you selected. If the payload is not listed, then you can click on ‘Browse All’ and then ‘All Payloads (Testing)’ and find the closest match to the balloon you are trying to track.

Once you have audio being routed to dl-fldigi, you will see the waterfall active. This gives a visual representation of what the radio is hearing. When you tune the radio and spot the signal you’re interested in, you can click on the center of the signal in the waterfall to attempt decoding. I have found that the most reliable decoding happens with the center of the signal is around the 1500 mark. Successful decoding results in the telemetry bar going green or turns red if the signal was corrupted. With an RTTY signal, it’s a good idea to have the AFC set on in the bottom right hand corner of the dl-fldigi panel. When you successfully decode and upload telemetry with dl-fldigi, your callsign that is set in the operator options appears in the info panel for that payload on the SpaceNear.us page.

Before using dl-fldigi, be sure to set your details, especially your position, in the options. To set your personal details, go to Configure – Operator. To set your location, go to DL-Client – Configure – Location In here, the Latitude and Longitude needs to be set to place your icon in the right position on the map. You can find your Lat/Lon on Google Maps Right-click on your physical location and then ‘What’s here?’ and your Lat/Lon in decimal will appear in the search bar. You can cut’n’paste these values into dl-fldigi.

For further information and illustrations, there is a great page on the UKHAS website.

Steve Smith

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One Comment

I find it beneficial, as soon as I start DL-FLDIGI, to get a copy of the latest flights … on the Menu bar, click on ‘DL Client’ and then on ‘Refresh flight docs’. This ensures that the most recent info is available in your program so that you can select the correct flight from the ‘Flight’ tab.

Also, when decoding an RTTY signal it is most useful to increase the Receive filter bandwidth. The default value is about 60, but I prefer to increase this to over 200 (maybe 250) so that the AFC (automatic frequency control) finds it easier to track the signal as it drifts up and down. The filter setting is found as follows … right-click on the RTTY legend in the bottom left corner, and it is the slider control at the bottom of the pop-up window.

Finally, in the paragraph concerning RTTY, you mention setting the ‘AGC’ value in the bottom right corner … that should be ‘AFC’ – automatic frequency control.